<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Error handling</title><link rel="stylesheet" type="text/css" href="manual.css"><meta name="generator" content="DocBook XSL Stylesheets V1.76.0"><link rel="home" href="index.html" title="JpGraph Manual"><link rel="up" href="ch24.html" title="Chapter 24. Linear Barcodes (One Dimensional Barcodes)"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Error handling</th></tr><tr><td width="20%" align="left"> </td><th width="60%" align="center">Chapter 24. Linear Barcodes (One Dimensional Barcodes)</th><td width="20%" align="right"> </td></tr></table><hr></div><div class="sect1" title="Error handling"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2596419"></a>Error handling</h2></div></div></div>
            
            <p>The barcode module uses the standard library error handling which mean that in
                case of an error (most likely that the data validation fails) an exception will be
                raised. Errors can be handled in two ways.</p>
            <p>
                </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
                        <p>By enclosing the script in a <code class="code">try { ... } catch { ... }</code>
                            statement</p>
                    </li><li class="listitem">
                        <p>By installing a custom default error handler with
                                <code class="code">set_exception_handler()</code> when the library throws an
                            error the specified error handler will be called with an instance of the
                                <code class="code">JpGraphException</code> class.</p>
                    </li></ol></div><p>
            </p>
            <p>The following code snippet shows an example of using a try-catch statment</p>
            <p>
                </p><div class="hl-main"><table class="hl-table" width="100%"><tr><td class="hl-gutter" align="right" valign="top"><pre>1
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</pre></td><td class="hl-main" valign="top"><pre><span class="hl-inlinetags">&lt;?php</span><span class="hl-code">
</span><span class="hl-reserved">try</span><span class="hl-code"> </span><span class="hl-brackets">{</span><span class="hl-code">
    </span><span class="hl-var">$encoder</span><span class="hl-code"> = </span><span class="hl-identifier">BarcodeFactory</span><span class="hl-code">::</span><span class="hl-identifier">Create</span><span class="hl-brackets">(</span><span class="hl-identifier">ENCODING_CODE39</span><span class="hl-brackets">)</span><span class="hl-code">;
    </span><span class="hl-var">$e</span><span class="hl-code"> = </span><span class="hl-identifier">BackendFactory</span><span class="hl-code">::</span><span class="hl-identifier">Create</span><span class="hl-brackets">(</span><span class="hl-identifier">BACKEND_IMAGE</span><span class="hl-code">,</span><span class="hl-var">$encoder</span><span class="hl-brackets">)</span><span class="hl-code">;
    </span><span class="hl-var">$e</span><span class="hl-code">-&gt;</span><span class="hl-identifier">Stroke</span><span class="hl-brackets">(</span><span class="hl-quotes">'</span><span class="hl-string">abc123</span><span class="hl-quotes">'</span><span class="hl-brackets">)</span><span class="hl-code">;
</span><span class="hl-brackets">}</span><span class="hl-code"> </span><span class="hl-reserved">catch</span><span class="hl-brackets">(</span><span class="hl-code"> </span><span class="hl-identifier">JpGraphException</span><span class="hl-code"> </span><span class="hl-var">$e</span><span class="hl-code"> </span><span class="hl-brackets">)</span><span class="hl-code"> </span><span class="hl-brackets">{</span><span class="hl-code">
        </span><span class="hl-reserved">echo</span><span class="hl-code"> </span><span class="hl-quotes">'</span><span class="hl-string">Error: </span><span class="hl-quotes">'</span><span class="hl-code"> . </span><span class="hl-var">$e</span><span class="hl-code">-&gt;</span><span class="hl-identifier">getMessage</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-code">.</span><span class="hl-quotes">&quot;</span><span class="hl-special">\n</span><span class="hl-quotes">&quot;</span><span class="hl-code">;
</span><span class="hl-brackets">}</span><span class="hl-code">
</span><span class="hl-inlinetags">?&gt;</span></pre></td></tr></table></div><p>
            </p>
            <p>The code when run will give the error</p>
            <p>
                </p><pre class="screen">Error: Data validation failed. Can't encode [abc123] using encoding "CODE 39" </pre><p>
            </p>
            <p>The problem with the input data string is that Code 39 does not support encoding
                lower case letters. In the case some error handling is still needed but the image
                error should be displayed it is possible to re-raise the original exception as the
                following example shows</p>
            <p>
                </p><div class="hl-main"><table class="hl-table" width="100%"><tr><td class="hl-gutter" align="right" valign="top"><pre>1
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</pre></td><td class="hl-main" valign="top"><pre><span class="hl-inlinetags">&lt;?php</span><span class="hl-code">
</span><span class="hl-reserved">try</span><span class="hl-code"> </span><span class="hl-brackets">{</span><span class="hl-code">
    </span><span class="hl-var">$encoder</span><span class="hl-code"> = </span><span class="hl-identifier">BarcodeFactory</span><span class="hl-code">::</span><span class="hl-identifier">Create</span><span class="hl-brackets">(</span><span class="hl-identifier">ENCODING_CODE39</span><span class="hl-brackets">)</span><span class="hl-code">;
    </span><span class="hl-var">$e</span><span class="hl-code"> = </span><span class="hl-identifier">BackendFactory</span><span class="hl-code">::</span><span class="hl-identifier">Create</span><span class="hl-brackets">(</span><span class="hl-identifier">BACKEND_IMAGE</span><span class="hl-code">,</span><span class="hl-var">$encoder</span><span class="hl-brackets">)</span><span class="hl-code">;
    </span><span class="hl-var">$e</span><span class="hl-code">-&gt;</span><span class="hl-identifier">Stroke</span><span class="hl-brackets">(</span><span class="hl-quotes">'</span><span class="hl-string">abc123</span><span class="hl-quotes">'</span><span class="hl-brackets">)</span><span class="hl-code">;
</span><span class="hl-brackets">}</span><span class="hl-code"> </span><span class="hl-reserved">catch</span><span class="hl-brackets">(</span><span class="hl-code"> </span><span class="hl-identifier">JpGraphException</span><span class="hl-code"> </span><span class="hl-var">$e</span><span class="hl-code"> </span><span class="hl-brackets">)</span><span class="hl-code"> </span><span class="hl-brackets">{</span><span class="hl-code">
    </span><span class="hl-identifier">JpGraphError</span><span class="hl-code">::</span><span class="hl-identifier">Raise</span><span class="hl-brackets">(</span><span class="hl-var">$e</span><span class="hl-code">-&gt;</span><span class="hl-identifier">getMessage</span><span class="hl-brackets">(</span><span class="hl-brackets">)</span><span class="hl-brackets">)</span><span class="hl-code">;
</span><span class="hl-brackets">}</span><span class="hl-code">
</span><span class="hl-inlinetags">?&gt;</span></pre></td></tr></table></div><p>
            </p>
            <p>The line</p>
            <p>
                </p><div class="hl-main"><table class="hl-table" width="100%"><tr><td class="hl-gutter" align="right" valign="top"><pre>1
</pre></td><td class="hl-main" valign="top"><pre><span class="hl-code">JpGraphError::Raise($e-&gt;getMessage());</span></pre></td></tr></table></div><p>
            </p>
            <p>will display the image error as shown in <a class="xref" href="ch24s06.html#fig.barcode-validation-error" title="Figure 24.5. Image error - Failed barcode data validation">Figure 24.5. Image error - Failed barcode data validation</a></p>
            <p>
                </p><div class="figure"><a name="fig.barcode-validation-error"></a><p class="title"><b>Figure 24.5. Image error - Failed barcode data validation</b></p><div class="figure-contents">
                    
                    <div class="mediaobject"><img src="images/barcode_data_validation_failed.png" alt="Image error - Failed barcode data validation"></div>
                </div></div><p><br class="figure-break">
            </p>
            <p>In the command line barcode utility ( <a class="xref" href="ch24s07.html" title="Generating barcodes on the command line">Generating barcodes on the command line</a>) the alternative method of installing a different default error handler can be
                seen.</p>
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